The purpose of this project is to develop animal model of bioprosthetic cardiac valve failure and to utilize this animal model system to evaluate the pathologic alterations and hemodynamic dysfunction which develops in the values. We have shown that bioprosthetic valves implanted in juvenile sheep demonstrate the same pathologic alternations of degeneration and calcification as those implanted in humans; however, the development of these alterations is accelerated in sheep as compared to humans. Nearly 500 procine aortic or bovine pericardial bioprosthetic values from nine different sources have been implanted in the animal model system to assess the characteristics of the pathologic changes, to compare the alterations in different types of values, to compare the alterations ocurring in valves implanted in the mitral versus the tricuspid positions, and to evaluate valves treated prior to implantation with processes to retard or eliminate the calcification process. Due to these types of observations, clinical trials have been initiated with one new type of bioprosthetic valve. Equally important, if not more so, at least five types of valves have been rejected from consideration for clinical use. The model is additionally being utilized to validate ultrasonic techniques, including color encoded 2-D Doppler, for the characterization of bioprosthetic, mechanical, and synthetic leaflet valve velocity/flow profiles and for the noninvasive detection of valve failure.